Studies of behavioral and pharmacological treatments for autism spectrum disorders (ASD) are increasing at a rapid pace. However, demonstration of treatment effects has been limited by a lack of psychometrically sound measurement tools that are sensitive to change in core symptoms of ASD. In order to meet this need, the current team of researchers has developed a new tool, the Autism Impact Measure (AIM), which uses a novel approach designed to be sensitive to incremental changes in ASD symptoms. Unlike existing ASD measures, the AIM assesses the frequency of symptom occurrence using a 2-week recall period and a 5-point response format, allowing the measure to track incremental change over shorter periods of time. In addition, the AIM assesses the impact of ASD symptoms, allowing for identification of symptoms that have the most significant impact on actual functioning. This novel two-pronged approach has the potential to inform both treatment outcome research and clinical practice. Preliminary results from our initial multi-site study of psychometric properties indicate strong reliability and validity. The aims of the current project are 1) to further examine construct validity, 2) to examine the measure's sensitivity to change following treatment, and 3) to begin development of a modified teacher-report version. Data will be collected across three sites nationwide, and sensitivity to change will be established by collecting data pre-, during, and post-treatment among three different well-established treatments for ASD. The proposed team of investigators is well-poised to conduct this project, and includes a national network of collaborators with a proven track-record of multi-site ASD research and expertise in measure development and psychometrics. The AIM represents a novel measurement approach in the autism field and is highly relevant to clinical care and research. A major goal across federal health agencies is to improve the lives of children with ASD by developing interventions that target core symptoms of the disorder, and the development of a reliable and valid treatment-outcome measure has the potential to enhance the pace of treatment-outcome research.